Debt - Summary of Variable Rates (Details)	12 Months Ended
	Dec. 31, 2017
Prime rate | U.S Revolving Credit Facility | Minimum
Line of Credit Facility [Line Items]
Debt instrument basis spread on variable rate (as a percent)	0.00%
Prime rate | U.S Revolving Credit Facility | Maximum
Line of Credit Facility [Line Items]
Debt instrument basis spread on variable rate (as a percent)	0.50%
Federal funds rate | U.S Revolving Credit Facility | Minimum
Line of Credit Facility [Line Items]
Debt instrument basis spread on variable rate (as a percent)	0.00%
Federal funds rate | U.S Revolving Credit Facility | Maximum
Line of Credit Facility [Line Items]
Debt instrument basis spread on variable rate (as a percent)	0.50%
LIBOR | U.S Revolving Credit Facility | Minimum
Line of Credit Facility [Line Items]
Debt instrument basis spread on variable rate (as a percent)	0.00%
LIBOR | U.S Revolving Credit Facility | Maximum
Line of Credit Facility [Line Items]
Debt instrument basis spread on variable rate (as a percent)	0.50%
LIBOR | German Revolving Credit Facility | Minimum
Line of Credit Facility [Line Items]
Debt instrument basis spread on variable rate (as a percent)	1.50%
LIBOR | German Revolving Credit Facility | Maximum
Line of Credit Facility [Line Items]
Debt instrument basis spread on variable rate (as a percent)	2.00%